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Thread: Running rich on idle and WOT

  1. #1
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    Default Running rich on idle and WOT

    I apologize cause i know this subject has been touched on so many times but i'm really stuck here.

    I get nasty smells (guessing it's a rich condition) from my 1977 280z at idle and WOT, smells fine when cruising. it used to smell during cruising as well however went away after getting my EGR to work properly.


    Coolant sensor - all within range according to FSM

    New AFM (or rebuilt one MSA sells)

    All fuel hoses replaced, fuel pressure (~29psi at idle, ~33psi with throttle)

    Adjusted TPS to break from idle with slight throttle and connect full enrichment at almost full throttle (checked fine for continuity at ECU at idle and WOT)

    New distributor vacuum advance

    Replaced all vacuum hoses - I checked w/ pump and recall they were were within specs (I used Atlantic Z for readings)

    New thermal vacuum valve, BPT Valve and EGR valve

    With the cold start valve, I ran car for a few weeks disconnected, noticed car would crank more during morning starts, slightly better gas mileage (maybe 1 or 2mpg better, however my MPG is pretty inconsistent so I'm not sure if it was the CSV or not), still got rich smells at idle and WOT.

    Thermotime sensor - As with the CSV, the MPG or smells weren't all that different with or without it connected outside of the cold starting, which makes me assume the system works fine. Right?

    Air regulator - replaced maybe a year ago

    Fuel pressure regulator - checked by removing the vacuum from bottom outlet and fuel pressure jumps to about 40psi

    BCDD - I think it's broken. If I engage the clutch when driving or coming to a stop, idle will drop stumble and drop to about 600rpm then stabilize around 900rpm. i have the idle set slightly higher at 900rpm to compensate the faulty BCDD.

    Spark plugs are fairly new. I've checked them after a drive and they do not look sooty or black. Didn't look all that bad when I replaced the prior ones either.

    As noted, all for mentioned were also checked at ECU when applicable, per the fuel injection book. Only one I think I didn't check was the cold start system. Lastly, I get anywhere from 13 - 15mpg. It seems to get consistent 15mpg marks ever since i fixed my EGR.

    Any help or suggestions would be appreciated.
    Last edited by UR2H; 09-21-2014 at 02:11 PM.

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    You didn't mention ignition timing or adjusting valve lash. Those are two basic tuneup procedures. Very important too.

    Also, the CSV only gets voltage during starting. So, unless it is leaking, it will have no effect on MPG.

    The idle drop when you press the clutch is kind of typical of running rich. My car does that if I have it tuned rich (potentiometer). Timing affects that also. 40 psi is 10% too high on fuel pressure. But the gauges available today are often inaccurate. Might try another gauge.

    The first two things that I would do is to check and set the timing, confirming that it does advance when RPM increase, like it should, and check and set valve lash. Also check your cam timing when you have the valve cover off.

    And, in the future, the actual numbers are nice to see. "Within range" doesn't mean as much.
    1976 280Z, with some minor modifications

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    Valve lash is something I've been meaning to check. I guess that's my mission for this week.

    As for timing, I don't have a timing gun but When they checked it for the last smog check, they read at 9 BTDC.

    Sucks I can't check the timing advance but I will take a look at the mechanical advance just to make sure the reluctor is moving and that the RPMs increase accordingly with vacuum.

    Also i just went to recheck the fuel pressure regulator. It jumps to 37psi when removing the vacuum. I'm going off memory with my findings. I guess I should've written down all my readings rather than going off memory and saying things are "within range"

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    The thing about the EFI system is that you can be at the limits of in-range and if they all add up the wrong way, you'll be rich or lean. A few ohms, a psi or two, a vacuum leak, a mis-adjusted AFM. They can add up.

    The best place to measure coolant sensor resistance is at the ECU connector. It's what the ECU sees. Plus, the ECU connector itself can get corroded, adding resistance. The ECU is not really in a good spot, a lot of water leaks pass by its location.
    1976 280Z, with some minor modifications

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    Tommy, where about's are you in CA? If you are close I can help you on some of these things.

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    I am a bit out of the way from Ventura. I am in San Jose

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    Checked the distributor mechanical vacuum advance and seems to be working properly. I unhooked the vacuum line from the throttle chamber,hooked up my pump, added 10hg and rpm rose about 2000rpm.

    Also checked vacuum by disconnecting the hose from the brake booster and found my vacuum is a steady 18hg at idle, and stabilizes at about 21hg at high rpm.

    Hey zed head, my afm is rebuilt one from MSA and apparently set to manufacturer specs. do you think I would need to adjust it? I haven't opened it figuring I don't need to worry about it. And yes, I checked my coolant sensor resistances at the ecu connector. I'll give all the resistance and continuity checks at the connector another go round and make sure to record my readings this time.

    Im really looking forward to the valve adjustment. It's never been done and I've never done one. Seems easy enough though. Engine was rebuilt by Nissan but was 50k miles ago. Guess it's way overdue.

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    I have an MSA AFM and it works fine. But for a while I thought that it ran rich. But after tuning and cleaning and fixing a variety of odds and ends I put it back on (I had switched to a junk yard AFM that was leaner), I found that it works great now. No flat spots.

    I would make sure that everything is to spec. first. And I would use an adjustable FPR to lower fuel supply before I messed with the AFM. I think that when you move the preload on that spring you change the position of the air flow - enrichment curve differently than using fuel pressure or a potentiometer. The starting and ending points move, since it's preloaded (low RPM) and it goes full enrichment before maximum air flow is achieved (WOT high RPM). And it's a weird load on the spring with the air acting on a lever, the vane. I'm not sure that changing spring preload simply makes things richer or leaner everywhere.

    When you use the potentiometer (richer) or fuel pressure (richer or leaner) you keep the shape but move the whole thing up or down.

    My logic could be off, but there are other ways to get to where you want to be.
    1976 280Z, with some minor modifications

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    Update:

    Did a cold valve adjustment 0.008 for my intake and 0.010 for my exhaust. Most of my intake clearance were good, only had to adjust 2 of them. All of my exhaust valves were tight and needed adjustment.

    Put it all back together but now the valve ticking noise is a lot louder than it was before. Could the louder ticking be From loosening all the exhaust valves? Car does seem to run better now than it did before. Doesn't smell as much either. I'll do a hot adjustment tomorrow but should I be worried about the valve ticking being significantly louder?
    Last edited by UR2H; 09-23-2014 at 10:25 PM.

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    On a side note, I somehow snapped off one of my front upper strut mount studs when I was tightening it back on. Had to take off the upper strut brace so I could remove the rocker cover. On a scale of 1-10, how dangerous do you think it'd be to drive around with two studs instead of three?
    Last edited by UR2H; 09-23-2014 at 10:29 PM.

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    Quote Originally Posted by UR2H View Post
    On a side note, I somehow snapped off one of my front upper strut mount studs when I was tightening it back on. Had to take off the upper strut brace so I could remove the rocker cover. On a scale of 1-10, how dangerous do you think it'd be to drive around with two studs instead of three?

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    FWIW - i found the hot lash adjustment to be much more accurate than the cold.
    after a hot adjust, the valves are still spot on for my re-check days later, but with the cold they're kinda all over the place. i think the cold is just to get you in the ballpark when re-building but the hot is the real deal.

    just my .02
    '78 280z - Daily driver/work in progress...

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    Drove around, got my engine hot and adjusted to specs.

    Should've asked this earlier but how tight am I supposed to adjust?
    For instance, on an intake clearance, should -

    (1) .010 go in relatively easy and .011 can go in but with some force

    OR

    (2) .010 go in with some force and .011 not go in unless I really jam it in there?

    Cause I adjusted with by (1) and maybe my valve "ticking" is due to loose adjustments?

    Also I noticed the wear on my lash pad is uneven. On one side/half, the feeler won't have as much friction as on the other side. Is this normal wear and tear? And am I using the side of the lash with the stronger friction as the primary feeler contact for adjusting?

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